Changes of cortical and caudatal unit activity accompanying operant slowing of the extension phase of reaching in rats.

Activity of neurons in the motor cortex (n = 36) and caudate nucleus (n = 72) was studied in 7 rats trained to slow down reaching into a narrow horizontal tube equipped with an axially moving piston. Overtrained rats succeeded in obtaining reward by reducing extension velocity of 30 to 60% reaches below 50% of the normal value. The difficulty of the task was reflected in the amplitude of perireach histograms which showed peaks and troughs corresponding to the main phases of the movement. Perireach distributions of excitatory and inhibitory unit reactions were similar in the contralateral motor cortex and caudate nucleus of trained rats, but the inhibitory responses started later and were shorter lasting than during standard reaching in naive animals. It is suggested that the task requires tight cortical control of the postural and local movement components manifested by synchronous activation of caudatal and cortical neuronal populations.